Daytime sleep patterns may aid narcolepsy diagnosis, study finds
Test finds people with narcolepsy spend more time in REM sleep phase
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Excessive daytime sleepiness is a sign of narcolepsy. (Image by iStock)
Two features of rapid eye movement (REM) sleep, the sleep stage characterized by high brain activity and vivid dreaming, may help distinguish people with narcolepsy from those with other conditions that cause excessive daytime sleepiness.
That’s according to a study that measured aspects of REM sleep using a multiple sleep latency test (MSLT), a daytime test that measures how quickly someone falls asleep during a series of naps and how often they enter the REM phase. Results showed that people with narcolepsy type 1 (NT1) and type 2 (NT2) spent more time in REM sleep and had more REM sleep without atonia (RSWA, abnormal persistence of muscle activity during REM sleep) than people with other causes of excessive sleepiness (hypersomnia).
The researchers said the two measures could “represent promising candidate biomarkers in distinguishing between narcolepsy subtypes and other hypersomnias.” The findings may be particularly useful for NT2, which can be difficult to distinguish from idiopathic hypersomnia.
The study, “Rapid Eye Movement Sleep-Related Indicators with Promising Performance in Diagnosing Narcolepsy,” was published in Nature and Science of Sleep.
Narcolepsy is a sleep disorder marked by excessive daytime sleepiness (EDS). NT1, the most common form of narcolepsy, is caused by a loss of brain cells that make orexin (also called hypocretin), a chemical that helps regulate wakefulness. It is usually more severe and associated with cataplexy (sudden episodes of muscle weakness). In NT2, cataplexy is absent, and hypocretin levels are generally normal.
Diagnosis can be a challenge
Narcolepsy symptoms also include sleep paralysis (a temporary inability to move or speak during sleep-wake transitions), sleep-related hallucinations, and REM sleep behavior disorder (RBD). These symptoms are linked to disrupted regulation of REM sleep, a time when most muscles temporarily relax to prevent people from acting out their dreams.
Diagnosing narcolepsy can be challenging. In NT1, cataplexy may be subtle or appear in unusual ways, making it difficult to recognize. The challenge is particularly pronounced in NT2, where symptoms, particularly EDS, overlap with other causes of excessive sleepiness.
Narcolepsy diagnosis relies heavily on polysomnography (PSG), an overnight sleep study, followed by the MSLT. Because these measures can be inconsistent or nonspecific, researchers in China investigated whether other features of REM sleep captured during routine sleep testing could help distinguish narcolepsy, particularly NT2, from other causes of excessive daytime sleepiness.
The prospective study involved 206 people evaluated for excessive daytime sleepiness at West China Hospital between January 2020 and March 2023. Eighty-seven had NT1, 27 had NT2, and 92 had other causes of excessive sleepiness, including depression and idiopathic hypersomnia.
All participants underwent an overnight PSG followed the next day by an MSLT, which included five opportunities to nap, each two hours apart. The researchers compared REM-related symptoms and several REM sleep measures collected during both tests.
Clinical symptoms clearly set NT1 apart, with these participants generally reporting more severe EDS, sleep paralysis, sleep-related hallucinations, and RBD symptoms. People with NT2, however, could not be distinguished from those with other causes of excessive sleepiness based on symptoms alone.
A clearer difference emerged during MSLT. Across the five naps, people with NT1 spent a median of 36.75 minutes in REM sleep and those with NT2 22.30 minutes, while the median was zero among people with other causes of excessive sleepiness.
A cutoff of 11.91 minutes of daytime REM sleep identified NT1 with 87% sensitivity and 93% specificity — meaning it correctly identified 87% of people with NT1 and correctly ruled it out in 93% of those without it. For NT2, a cutoff of 8.41 minutes showed a 90% sensitivity and 88% specificity. The measure also distinguished NT2 from idiopathic hypersomnia, with 89% sensitivity and 86% specificity at a cutoff of 7.18 minutes.
RSWA during the MSLT provided another potential marker. The any RSWA index, which captures any abnormal muscle activity during REM sleep, was higher in both narcolepsy groups. At a cutoff of 36.61%, it identified NT1 with 91% sensitivity and 80% specificity, while a cutoff of 18.83% identified NT2 with 99% sensitivity and 75% specificity.
Neither daytime REM sleep duration nor the any RSWA index added significant diagnostic value beyond standard MSLT measures. The researchers said this may be because the standard MSLT measures were already used to classify participants and therefore captured much of the same diagnostic information.
Yet both measures independently showed a strong ability to distinguish people with narcolepsy from those with other causes of excessive sleepiness. “We propose the daytime REM sleep duration and any RSWA index from MSLT as promising markers for narcolepsy diagnosis, particularly for NT2,” the researchers wrote.
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